Copending and commonly assigned U.S. patent application Ser. No. 08/075,433, filed on Jun. 14, 1993, entitled "Integrated Rotary Printer Drive System" by Orilick et al., the contents of which are herein incorporated by reference, describes a rotary printer drive system having a print head that includes a light-emitting-diode (LED) array. The LED array, located within a rotating print drum, is focused with an optical system onto a photographic media fixed to a concentrically mounted cylindrical shoe. The LEDs are modulated so as to raster scan image information onto the media as the drum rotates and is axially translated through the shoe. Data is transmitted to the LED array via a rotary transformer channel at a rate dictated by the measured rotational rate of the print drum.
As described in copending and commonly assigned U.S. patent application entitled "Method and Apparatus for Exposing Photosensitive Media with Multiple Light Sources", by D. H. Smith et al., Attorney Docket No. 66,013, the contents of which are herein incorporated by reference, the LED array is preferably formed as an integrated structure having a two dimensional array of LED's arranged in columns and rows, wherein the columns and rows are arranged at a spatial frequency less than the spatial frequency of image lines and image pixels to be produced. The geometry of this "sparse" LED array is such that multiple physical pixel locations on the media are simultaneously exposed by individual LED elements of the print head at any time. As the print head scans along a line, adjacent pixels are uniquely exposed and each pixel is redundantly exposed with its unique information in non-contiguous pixel time intervals.
The most direct method of driving the LEDs of the sparse array is to access an image data source and transmit data pertaining to each of the multiple pixels being exposed in the current pixel clock interval for each such interval. This method, however, would require the printing system to have very high transmission bandwidth and data access capacities, in order to avoid limiting image throughput rate and machine productivity.
In view of the above, it is an object of the invention to provide an improved data transmission system for supplying image data to the sparse array.